Enzymes Flashcards
What are enzymes?
- Biological catalysts - speed up chemical reactions without being used up during the reactions
- 3D globular proteins with specific tertiary structure
- Specific - they only catalyse one type of reaction and can only work on one specific type of substrate molecule
- Active site is complementary in shape of their specific substrate
What is the lock and key model?
- Says the active site is a specific shape which is complementary to the shape of its substrate
- The binding of the substrate to the active site allows bonds to break or form more easily
What is the induced fit model?
- Substrate collides with the active site
- Active site moulds around the substrate molecule and it is held in position by oppositely charged groups on the amino acid in the active site
- Enzyme - substrate complex formed
- Change in enzyme’s 3D shape places strain on the substrate molecule
- Strain weakens chemical bonds making them break more easily
- Enzyme - product complex formed
- Product no longer fits into the active site and is released
What is a catabolic reaction?
Involve the break down of hydrolysis of larger molecules to smaller ones
What is an anabolic reaction?
Involve larger molecules being made by the condensation of smaller molecules
What are intracellular enzymes?
Enzymes which remain inside the cell
What are extracellular enzymes?
Enzymes which are secreted from cells to function
What is an enzyme’s turnover number?
The max amount of substrate molecules it can convert to product molecules per unit time
What is a TIME, RATE and CONC graph?
Time graph - Shows how long the reaction takes to occur in seconds
Rate graph - Shows how fast the reaction occurs (s-1)
Conc graph - Shows how much product is produced
What is the effect of temperature on enzymes?
Low temps - Longer, do not have a lot of kinetic energy, few successful collisions = few enzyme substrate complexes
Optimum temp - more kinetic energy, more successful collisions, more e-s complexes
Higher temps - enzyme molecules vibrate more, causes H bonds within enzymes to break, 3D globular shape is altered so active site changes, less e-s complexes formed = enzyme denatures
What is the effect of pH on enzymes?
Optimum temp - Charges of active site are complementary to the charges on the substrate, more no. successful collisions, more e-s complexes
Small changes - Reversible changes, fewer successful collisions, fewer e-s complexes
Extreme pH - interfere with ionic bonds causing them to break, 3D globular shape is altered as well as active site, enzyme denatures
What are the effects of changing substrate concentration?
Low conc - fewer substrate molecules, fewer e-s complexes formed, fewer products produced
Higher conc - more successful collisions, more e-s complexes formed, more products produced
Very high conc - all enzymes active sites are occupied at any one time, conc will not decrease (enzymes limiting)
What are the effects of changing enzyme concentration?
Low conc - fewer active sites are available, fewer e-s complexes formed, fewer products produced
Higher conc - more available active sites, more successful collisions, more e-s complexes, more products
Very high conc - more active sites than substrate so increasing enzyme conc does not change rate
What is a competitive inhibitor?
- Compete with normal substrate at active site
- Structure is similar to substrate
- Prevents formation of e-s complexes
- Adding more substrate can reduce effect
What is a non competitive inhibitor?
- Binds to allosteric site
- Irreversible
- e.g Cyanide
How are industrial enzymes made?
- Produced by culturing microbes in fermentation vessels, microbes produce enzymes as part of their normal metabolic activity
Why are enzymes used in large scale industrial production?
Biological catalysts - speed up rate of reaction by lowering activation energy
Few side reactions so less waste products are formed
What are immobilised enzymes?
Enzymes which are held or stabilised in an INERT support or matrix e.g. cellulose
What are the advantages of immobilised enzymes?
- enzymes are easily recovered so can be used over and over again, reducing costs
- product is not contaminated by the enzyme
- polymer matrix creates a microenvironment for the enzyme so it is more stable
- used in continuous processes
- several enzymes, with different optima can be used at the same time
What are the methods of immobilising enzymes?
- adsorption = attached to glass, beads, clay particles or collagen
- entrapment = enzyme entrapped in cellulose mesh or alginate beads
- chemically bond - chemically bonded-cross linked using Glutaraldehyde
What are the disadvantages of immobilisation?
- in adsorption, enzyme may become detached
- presence of the alginate gel alters the shape of the active shape reducing activity compared to free enzymes
- chemically bonding the enzyme is a complex and expensive process
- any contamination is costly because the whole system has to be shut down and the vessel re-sterilised
